1. Field of the Invention
The present invention concerns a photointerruptor for use in a light transmission type rotary encoder capable of obtaining optical pulse signals in accordance with an angle of rotation of a pulse scale having a plurality of code patterns formed thereon and, more specifically, it relates to a photointerruptor for use in a light transmission type rotary encoder which is suitably incorporated, for example, as a sensor for detecting a crank angle in an automobile engine.
2. Description of the Prior Art
Photointerruptors for use in light transmission type rotary encoders include a so-called device type photointerruptor in which a pair of light emitting device and a photoreceiving device are integrally resin-molded such that they are opposed on both sides of a code pattern on a pulse scale and a so-called optical fiber type photointerruptor in which a pair of light emitting optical fiber and a light receiving optical fiber are resin-molded such that their end faces are opposed to each other.
As shown later in FIG. 3 of the appended drawings, light emitting devices 31, 31 and photoreceiving devices 32, 32 are opposed on both sides of code patterns C.sub.1, C.sub.2 formed along the circumference of a pulse scale 1 in the device type photointerruptor.
However, when the device type photointerruptor is used, for example, to a light transmission type rotary encoder as a sensor for detecting a crank angle in an automobile engine, since the photointerruptor is exposed to severe circumstances such as high temperature, violent vibrations, or electromagnetic noises in an engine room, there may be possibly caused degradation of the light emitting devices 31, 31 and the photoreceiving devices 32, 32, disconnection of power feed lines or signal lines, failure of contact in connection portions, etc. due to vibrations. Further, there is also a worry of misoperation caused by electromagnetic noises and no accurate detection of angle can be conducted.
On the other hand, in the optical fiber type photointerruptor, as shown later in FIG. 4, light emitting optical fibers 41, 41 and light receiving optical fibers 42, 42 are disposed, instead of the light emitting devices 31, 31 and photoreceiving devices 32, 32, on both sides of code patterns C.sub.1, C.sub.2 formed on a pulse scale such that end faces of the fibers are opposed to each other.
When the optical fiber type photointerruptor is used for the light transmission type rotary encoder as the sensor for detecting the crank angle in an automobile engine, since the light emitting device and the photoreceiving device can be disposed at a position remote from the engine, the light emitting device and the photoreceiving device can be free from undesirable effects of high temperature or vibrations caused from the engine.
Further, since the optical fiber is electrically noninductive, there is also a merit of causing no misoperation due to electromagnetic noises.
However, in the conventional optical fiber type photointerruptor, if a plurality of code patterns are formed on the pulse scale 1 since light emitting optical fibers disposed on each of the code patterns are connected respectively to the light emitting devices, the number of parts such as the light emitting devices and the light emitting optical fibers is increased to make the structure expensive.
In particular, for improving the signal/noise (S/N) ratio by increasing the intensity of light entering the photoreceiving device as much as possible, it is required to use expensive light emitting devices having high power and high directionality, and the cost is increased remarkably if such expensive light emitting devices are used in plurality.
In addition, since free ends of the respective optical fibers 41, 42 to be connected with light emitting devices and the photoreceiving devices are extended to the outside of a photointerruptor main body 43, they have to be handled with a great care so as not to injure or flex the optical fibers 41, 42, for example, upon packaging or transporting the photointerruptor 43, and this enforces much inconveniency for the handling.
Furthermore, upon installing operation of the rotary encoder, wiring operations for connecting each of the optical fibers 41, 42 with the light emitting devices or the photoreceiving device, or bundling and fixing them are extremely troublesome. In addition, when the photointerruptor main body 43 is mounted to a narrow place, for example, in an engine room of an automobile, optical fibers 41, 42 may possibly be damaged or flexed.